1. Field of the Invention
The present invention relates to a planar motor used for a fine positional control of a stage of an optical microscope, for example.
2. Description of the Related Art
As a device for two-dimensionally driving a subject in X-Y directions so as to be positioned, an X-Y stage structured by combining a servo motor with a linear guide is well known.
As the aforementioned X-Y stage, an XYθ stage for linearly moving and turning the stage has been proposed, in which three sides of a square table are provided with linear actuators, respectively and output shafts of the respective linear actuators are connected to the corresponding sides of the square table (Japanese Unexamined Patent Application Publication No. 2002-341942).
In the aforementioned XYθ stage, the driving force is constantly applied to one of the connection parts of inclined linear guides even when only a first or second driving unit is driven by providing an inclination angle between the linear guide directions of the respective linear guides functioning as the direction motion guiding member connected with two linear actuators functioning as a pair of first driving units. The driving force is applied to at least two connection parts together with the connection part connected with the driving unit to supply the driving force with sufficient balance.
The XYθ stage is of semi-close control type having its linear actuator driven by, for example, a stepping motor for controlling movement positions of the X-axis and Y-axis, and the turning angle in accordance with the pulse number. As the accurate positional control is likely to be influenced by precisions of the parts that constitute the transmission mechanism and by the backlash upon transmission of the driving force, it is difficult for such XYθ stage of semi-close control type to achieve the highly accurate positioning.
The planar motor for controlling directions of the X-axis and Y-axis, and the turning angle has been proposed by the applicant of the present invention (Japanese Unexamined Patent Application Publication No. 2005-168154). According to the disclosure, the permanent magnet for the linear motor is attached to the movable stage, and a coil for linear motor is attached to the fixed stage, and electricity is applied to the coil to constitute the coreless linear motor that moves the movable stage in the directions of the X-axis, Y-axis, and θ. A cross-shaped common electrode is mounted on the movable stage, and a pair of fixed electrodes is provided to each end of the cross-shaped common electrode. Each displacement in the directions of the X-axis, Y-axis and θ is derived from the respective displacements in the electrostatic capacities of the capacitors formed between the cross-shaped common electrode and the fixed electrode. The positioning control in the directions of X-axis, Y-axis and θ may be executed based on the derived displacements in the respective directions.
According to the disclosure, the planar motor of thin and low vibration type is capable of executing a highly accurate positioning.
Unlike the generally employed motor, the planar motor disclosed in Japanese Unexamined Patent Application Publication No. 2005-168154 is suitable for the use in the device that requires accurate position control as it is capable of executing highly accurate positioning. In the case where the external force is applied to the stage although such force is relatively small, the stage is likely to move. As it is not intended to move the movable stage with relatively large force, it is unsuitable for the use as the mechanism for moving the stage that is required to have both accurate position control and the thrust force.
The use of a plurality of linear actuators may be considered to drive the movable stage in directions of the X-axis, Y-axis and θ so as to be moved with a large force. Because of the error in the combined parts or the backlash of the transmission mechanism which may influence the positioning control, and the semi-closed control mode, it is difficult for the aforementioned planar motor to establish the highly accurate position control.